Paper breadth re-humidifying method and equipment

Abstract

The invention relates to a method for rehumidifying a paper web (4), in which the web (4) is guided by means of a device (2) having a processing unit (10) for processing the web (4), in which the device (2) has a drying unit (12) for drying the web (4) downstream of the processing unit (10), in which the device (2) has a plurality of humidifying units (18, 20) downstream of the drying unit (12), the web (4) is re-humidified by means of a plurality of humidifying units in a plurality of stages by means of a humidifying agent, in particular by pre-humidifying the web (4) with a first humidifying unit (18) and re-humidifying the web (4) with a second humidifying unit (20) after a shortest dwell time (T), the shortest dwell time (T) being selected accordingly, the web (4) in the second humidification unit (20) has an improved rate of absorption of the humidification agent as a result of pre-humidification. The invention further relates to a device (2) for processing a paper web (4).

Description

Technical Field

[0001] The invention relates to a method for rehumidifying a paper web and a device for processing a paper web. Background Art

[0002] Examples of paper web converting plants include printing presses for printing such webs and corrugating plant for producing webs consisting of a plurality of paper layers, more precisely corrugated board webs.

[0003] In conjunction with the processing of paper webs, the webs are usually dried, for example after printing in a printing press. During drying, a significant amount of moisture (i.e. water) is removed from the paper, which is then appropriately replenished again under the framework of rehumidification. The problem here, however, is that paper has only a limited capacity to absorb the water applied to the web during the rehumidification process. As a result, it may not be possible to fully replenish the previously removed water. This then often leads to defects such as the formation of wrinkles, canning effects, streaks, etc. Such defects can lead to problems when the web is wound up at the end of the machine or when the web is directly handed over to a subsequent machine in an in-line process.

[0004] A method for moistening a moving printing material web is described in US Pat. No. 5,596,930 A. In this case, the moistening agent can be applied to the web in several steps. Summary of the invention

[0005] In view of this, the object of the present invention is to improve the rehumidification of a paper web. To this end, in particular, a correspondingly improved method and an improved device should be provided.

[0006] According to the invention, this object is achieved by a method having the features of claim 1 and by a device having the features of claim 15. Advantageous embodiments, improvements and variants are the subject matter of the dependent claims. The detailed descriptions relating to the method also apply to the device and vice versa. If the steps of the method are described below, advantageous embodiments of the device follow therefrom, i.e. they are designed to carry out one or more of these steps.

[0007] The core idea of ​​the invention is in particular multi-stage rehumidification, in which the rehumidification of the paper web is divided into a plurality of stages for applying a moistening agent to the web in each case. In this way, the effect that the pre-moistened web subsequently has a significantly higher water absorption rate than a non-pre-moistened web can be utilized, so that the paper can absorb significantly more moistening agent, in particular water, and thus more moisture.

[0008] The method according to the invention is used for rehumidifying a paper web, in particular also a method for operating a device for rehumidifying. In the following, without limiting the generality, reference is made to single-ply paper webs, i.e. paper webs in the narrow sense, but the invention is also applicable to other, in particular multi-ply paper webs, such as corrugated board webs or subsequent primary products of webs consisting of a plurality of paper single layers.

[0009] The web is guided by the system. For example, the web is unwound by an unwinder of the system, subsequently processed and finally rewound by a rewinder of the system or, alternatively, directly forwarded to a subsequent system. In the following, without limiting the generality, the system is assumed to be a printing press, but the content described here is fully applicable to all kinds of systems that process paper webs and carry out rehumidification in conjunction with them. This embodiment is also particularly advantageous if the system is, for example, a corrugated board system for producing corrugated board.

[0010] The device usually has a processing unit for processing the web. In addition, downstream of the processing unit, the device has a drying unit for drying the web (i.e. the processed web). The drying unit has in particular one or more hot air dryers and / or infrared dryers for drying. The processing method and the drying method are not involved for the time being. Generally, what is more important is that moisture is removed from the paper web in principle during the drying process. Under the framework of the method with the help of rehumidification, this moisture should be replenished as completely as possible. For this purpose, downstream of the drying unit, the device has a plurality of humidifying units, with the help of which the web (i.e. the dried web) is rehumidified with a humidifying agent in a plurality of stages. Accordingly, the dried web is re-supplied with moisture with the help of the humidifying unit by applying a humidifying agent to the web. In this case, the web is re-humidified with a moistening agent in several stages by pre-humidifying the web (also called preliminary moistening or "Pre-Wetting") with a first moistening unit and re-humidifying the web after a minimum residence time (also called "secondary moistening" or "Secondary Wetting") with a second moistening unit. Pre-humidification and re-humidification take place in particular on the same side of the web, in a suitable embodiment even on both sides.

[0011] The humidifier contains water, preferably mainly water (ie, ≥95% or even ≥99%) or even only water. Suitably, the water is soft water and / or deionized water as far as possible. In a particularly advantageous embodiment, the humidifier is a mixture of water and a humidifying additive, the humidifying additive preferably having a content of up to 1% by volume, particularly preferably a content of up to 0.1% by volume, which is usually sufficient for high-quality humidifying additives to achieve a minimum surface tension. The humidifying additive serves to reduce the surface tension of the water (e.g., from 72.7 mN / m (polar component: 51 mN / m, dispersive component: 21.7 mN / m) to 28.5 mN / m (polar component: 5.2 mN / m, dispersive component: 23.3 mN / m) at 20° C.), thereby further increasing the absorption rate. Optionally, the humidifier is additionally mixed with air or another inert gas (e.g., nitrogen).

[0012] The expression "A is upstream of B" and the corresponding expression "B is downstream of A" means that A is ahead of B along the web, i.e. the web first passes A and then B. Likewise, the term pairs "in front of / behind" and "in front of / behind" are used instead of "upstream / downstream".

[0013] For convenience, it is expressed here that the "web" is treated (processed, dried, humidified, etc.). This means that the web is processed step by step in sections, i.e. it is not processed first, then dried as a whole, and then humidified, but the web is guided continuously (i.e. in a pipeline) through the entire device, and the corresponding web sections are processed at the corresponding positions and then directly passed on.

[0014] The minimum residence time is now selected accordingly so that the web has a higher absorption rate of the moistening agent in the second moistening unit due to the pre-moistening (by the first moistening unit). In a suitable, but not mandatory embodiment, in particular for 3 g / m 2 The corresponding absorption rate of the humidifier is between 0.1s and 1s (i.e., 3g / (s*m 2 ) to 30g / (s*m 2)), while for other dosages, the corresponding absorption speed is used. In other words: the moistening agent is applied to the web by pre-humidification and is absorbed by the paper during the shortest residence time, making the web more hydrophilic after the shortest residence time. In this case, the principle is used that the moistening agent first forms a liquid film on the web during the pre-humidification process, which is not immediately absorbed by the paper due to the previous drying process, but at least partially stays there and requires at least a certain time to be completely absorbed by the paper. During this period, it can be said that the web is flooded with moistening agent, and it does not make sense to continue to supply moistening agent because it cannot be absorbed by the paper. The liquid film forms a corresponding barrier and limits the maximum absorption capacity of the paper. The transport of the web through the device and the available path also limit this maximum absorption capacity, because as soon as the web needs to be further processed or wound up, there must be no more moistening agent on the web and it must be removed if necessary.

[0015] Accordingly, the rehumidification is divided into multiple stages, that is, assigned to at least two humidification units, which then form the first rehumidification stage and the second rehumidification stage accordingly. Here, the actual target amount of humidifier is not used for prehumidification, but the amount of humidifier is reduced accordingly. The remaining humidifier will only be provided during rehumidification using the second humidification unit. However, since the web is now prehumidified here, the humidifier of the second humidification unit can be absorbed by the paper significantly faster (i.e., the absorption speed is increased) compared to without prehumidification, so that the web can absorb more humidifier in total on the same path compared to single-stage rehumidification. Similarly, this advantage is also reflected in the case of rehumidification using more than two stages.

[0016] Now, the shortest residence time is used in particular to wait for a re-humidification moment that is as favorable as possible. As mentioned above, the humidifying agent first forms a liquid film on the web during pre-humidification, and when the web reaches the second humidifying unit, this liquid film should be eliminated as much as possible. As long as there is a liquid film on the web, the absorption rate is actually equal to zero for the humidifying agent that continues to be applied, which will only increase after the liquid film is absorbed by the web. Therefore, it is preferably selected accordingly that the shortest residence time is such that when the web reaches the second humidifying unit, the humidifying agent applied by the first humidifying unit has been completely absorbed by the web. In particular, in this state and at this moment, the absorption rate will increase. In principle, it is also possible to simply remove any liquid film that may exist, for example using a rubber squeegee, but accordingly, the applied humidifying agent will be discarded in the process, resulting in them not being used.

[0017] The speed at which paper absorbs the humidifying agent is greatly influenced by the initial moisture content of the paper (i.e. the initial humidity). For example, paper that has dried out after passing through a drying unit absorbs water less quickly than pre-humidified paper. The reason for this is that the absorbed water molecules increase the hydrophilicity on the capillary walls of the paper. This reduces the contact angle and thus increases the absorption rate. This relationship is also summarized in the so-called Lucas Washburn equation (also referred to as the Washburn equation). According to this, with a reduced contact angle, the penetration depth per unit time increases and therefore the absorption rate increases. An increased penetration depth, increased hydrophilicity, a reduced contact angle and a reduced surface tension correspond in particular to an increased absorption rate.

[0018] The so-called hornification of paper is a particular problem with regard to the absorption rate of the web. Paper contains paper fibers that absorb water and release it again during drying. Hornification now refers to various fiber changes that occur during drying and re-moistening (i.e., actual changes in the paper fibers). Examples of such fiber changes include irreversible pore closure (reduction in specific surface area) due to hydrogen bond formation at adjacent cell walls or aggregation of microfibrils. Hornification is particularly irreversible. Hornification usually occurs during drying in a drying unit. Starting from hornification of the paper, it is particularly difficult to add moisture again, i.e., the absorption rate is particularly low. In particular, the method presented here now does not use only one humidifying unit to add as much water as possible in a given time and over a given path, but preferably first increases the absorption rate in a first stage by means of pre-moistening. Once the absorption rate has increased significantly, ideally reaching a suitable absorption rate threshold (e.g., the interval described above), further moisture is added to the paper in a second stage by means of re-moistening, but now with significantly higher efficiency than in hornified paper, so that overall more water is added to the paper in the same time and over the same path. Advantageously, due to the multi-stage rehumidification and the resulting increased moisture content of the paper, subsequent paper horn formation in the system can even be reduced or completely avoided, in particular during the drying process after rehumidification or during the drying process between two rehumidification stages.

[0019] As a result, significantly more moistening agent, in particular water, can be advantageously added to the web, so that a particularly high moisture content can be achieved accordingly. Similarly, the large amount of water lost during the drying process can be advantageously fully compensated, or even overcompensated if necessary. This allows corresponding reduction or complete elimination of defects such as streaks, wrinkles and canning effects during the transport and processing of the web in the system. It is important that the web is wrinkle-free, which can be ensured in particular by multi-stage rehumidification, both inside the system and at the end of the system. In addition, multi-stage rehumidification also has a positive effect on the shrinkage of the web in the system, in particular the shrinkage effect of the web caused by drying is significantly reduced by the subsequent rehumidification. In addition, multi-stage rehumidification can achieve differences in the moisture cross-section of less than 2%, in particular up to 1.3%, that is, the difference in moisture content at any two locations along the width of the web is less than 2%, or up to 1.3%. Usually, from a difference of 2%, so-called distortion occurs during further processing of the web in the corrugated board system, i.e. the corrugated board web is deformed. Finally, multi-stage rehumidification also enables high machine dynamics, especially in terms of web speed changes and order changes, because web shrinkage is compensated for at the right point as required. This is especially evident with suitable web width measurement sensors in the machine, and the advantages of precise cutting at the end during further processing in the corrugated board machine are also clear.

[0020] Preferably, the shortest residence time is in the range of 0.5s to 30s, particularly preferably in the range of 1s to 30s, but the upper limit of 30s is basically superfluous, that is, the shortest residence time is preferably at least 0.5s or at least 1s. Studies have shown that such a shortest residence time is sufficient to achieve the effect. The shortest residence time corresponds to the shortest path that the web passes between the first humidifying unit and the second humidifying unit. The conversion between the shortest residence time and the shortest path is carried out with the help of the web speed, that is, the speed at which the web is conveyed through the device. The web speed may vary from order to order. For the interval of 0.5s to 30s, with a preferred web speed of 100m / min to 450m / min, a nominal shortest path of between 1m and 225m is obtained, and advantageously, the shortest path is at least 2m in any case. In the maximum case, the shortest path is particularly significantly less than 225m, because typically, the running web (i.e., the path passed by the web) through the entire device is significantly less than 200m. Particularly preferably, the shortest distance between the first humidifying unit and the second humidifying unit is in the interval of 25 m to 50 m, in particular in the interval of 35 m to 40 m. Advantageously, these areas are still completely located inside the device. Thus, for the web speeds mentioned, a minimum residence time of approximately 4 s to 30 s, or 5 s to 24 s, is obtained.

[0021] Preferably, the shortest residence time between the first and second humidification phases is selected for the maximum web speed of the system (e.g. 450 m / min). Typically, a lower web speed does not cause problems in the following, since a longer residence time does not lead to a significant change in the water content in the paper. Accordingly, there is no upper limit for the shortest residence time, it being more important that the web is still moist when it reaches the second humidification unit and is not completely dry in any case, so that the absorption rate is increased for rehumidification. In addition, the amount of humidifier applied is appropriately set as a function of the web speed, so that the same amount of humidifier is always applied per unit time and per unit area in the event of a change in the web speed.

[0022] Typically, the amount of moisture that paper can absorb depends on the grammage of the paper (e.g., at 100 g / m 2 Up to 300g / m 2 The higher the grammage, i.e. the heavier the paper, the more water it can absorb. In addition, typically, higher grammage (especially >300g / m 2 ), the lower the dryness (observe moisture in %), so that high grammages generally do not require much rehumidification, but higher rehumidification amounts (especially > 3 g / m2) are possible without problems (i.e. especially without wrinkles) compared to lower grammages. 2 ). In an advantageous embodiment, the amount of moistening agent applied to the web per unit time by means of the moistening unit is therefore set as a function of the grammage of the paper, wherein the amount is also increased for increasing grammages. For the reasons mentioned above, the above relationship is not necessarily linear in particular and does not necessarily extend to very high grammages. Alternatively or additionally, the amount is set in a similar manner as a function of the type of paper. It is to be taken into account here that the binder and any other auxiliary agents in the paper as well as the porosity and initial moisture content of the paper, in general the type of paper, also influence the absorption rate, i.e. the ability of the paper to absorb water.

[0023] Preferably, each humidifying unit is used to apply a maximum of 3 g / m 2 This amount is ideal for machines of normal size and in the ranges mentioned above for the shortest residence time, and is also suitable for representative paper types and grammages. Depending on the grammages, one of the humidifying units will preferably apply 1 g / m 2 Up to 3g / m 2 of humidifying agent, wherein, as mentioned above, the amount used is also increased for higher gram weights. Thus, for at least two humidifying units, a total of up to 6 g / m 2Due to the multi-stage rehumidification, these humidifiers are also completely absorbed by the paper, thus achieving a correspondingly high moisture content. This is especially true for papers with particularly high grammage (especially >300g / m 2 ) or generally, a maximum of 4 g / m 2 , 5g / m 2 or 6g / m 2 or higher. Then, the total amount of humidifier will increase accordingly.

[0024] Suitably, a humidifying unit is used to apply at least 5 g / m 2 of moistening agent, or remoistening the web to a residual moisture content of at least 4% (here and in other cases wt %). Suitably, the moistening unit is used to remoisten the coated paper web to a residual moisture content of at least 4% to 5% and / or to remoisten the uncoated paper web to a residual moisture content of at least 5% to 7%. Suitably, in order to achieve a target moisture content (corresponding to a target residual moisture content) at the end of the system by means of rehumidification, a target moistening agent dosage is specified, which is then distributed to the moistening unit so that the moistening unit applies the target dosage to the web in total in multiple stages. The residual moisture content describes the moisture content in the web relative to the weight of the web. Depending on the grammage, preferably 5 g / m 2 Up to 8g / m 2 of dosage, wherein, as described above, the dosage is also increased for higher grammages. Alternatively or additionally, a residual moisture content in the range of 5% to 6% is preferred, in particular regardless of the grammages. The drying unit usually dries the web to a residual moisture content in the range of 2.5% to 3.5% (uncoated paper), which is then replenished by rehumidification to a residual moisture content of 1.5% to 3.5%, respectively, which, however, is typically not achieved by a single-stage rehumidification alone. Coated paper usually stores less moisture relative to the paper layer thickness than uncoated paper and is then typically dried to 1% to 1.5% (at an initial moisture content of 5%), whereupon a residual moisture content of 2.5% to 4% is replenished by rehumidification in order to achieve a moisture content of 4% to 5%.

[0025] Preferably, the humidifying units are respectively designed as spray bars. The advantages of the spray bars are particularly low installation space requirements and excellent economy. In addition, the spray bars are advantageously not operated in a circulating mode, so that only fresh humidifying agent is always applied to the web. In principle, other embodiments can also be considered, such as humidifying devices with rollers or spray discs, but the latter are less economical than spray bars and require significantly more installation space. As described here, the requirements for installation space are particularly important aspects of multi-stage rehumidification, because such designs require the humidifying units to be arranged at least at two different positions inside the device. However, since the design of the device is usually as compact as possible and many components are integrated in a narrow space, multi-stage rehumidification with large humidifying units (e.g., spray discs) cannot be easily adopted. Subsequently, especially for existing device designs, it cannot be installed without completely changing the device design. In comparison, the spray bar is particularly compact and can also be easily installed at different positions for existing devices without changing the original device design.

[0026] Furthermore, the use of a spray bar has the advantage that it typically has a plurality of nozzles arranged along the width of the web, so that uneven moisture distribution can also be easily compensated, i.e., homogenized, by selectively actuating individual nozzles (e.g., switching them on and off or setting the output of the humidifier).

[0027] There are many suitable embodiments for the arrangement of the humidifying unit in the device, of which several particularly preferred embodiments will be described below. These embodiments can also be combined with one another in principle.

[0028] The plant has at least one plant section, which contains the processing unit and the drying unit. However, depending on the specific embodiment, the plant may also have further plant sections, through which the web is guided in sequence, i.e. at the end of one plant section the web is directly handed over to the next plant section, so that the web can be processed several times and / or generally treated. Preferably, the last plant section is a winder which finally winds up the web into a roll, or a handover section which directly hands over the web to a subsequent plant without winding it up.

[0029] In a suitable embodiment, the humidifying unit is arranged downstream of the cooling unit of the system, which in turn is arranged downstream of the drying unit. The cooling unit after the drying unit serves to cool the web again. Now, the humidifying unit is not integrated in the cooling unit, but is arranged independently at another location, in particular downstream of the cooling unit.

[0030] In another suitable embodiment, the web is not dried, in particular likewise not processed, between the first humidifying unit and the second humidifying unit, but preferably only transported. Therefore, no further processing units or drying units are arranged between the first humidifying unit and the second humidifying unit, but the paper is merely absorbed by the humidifying agent. If the system has a plurality of system sections, the first humidifying unit and the second humidifying unit are accordingly arranged between two system sections, or at the beginning or end of a system section, or in a combined arrangement. The first humidifying unit and the second humidifying unit and the shortest path between them are also collectively referred to as two-stage humidifying sections.

[0031] In another suitable embodiment, the device has a plurality of device sections, each of which has a processing unit for web processing and a drying unit for subsequent web drying, and at least one of the humidifying units is arranged downstream of the corresponding drying unit, so that the web is humidified at least once after each drying, in particular before the next drying or before the end of the device. Unlike the two-stage humidifying section, the humidifying units are now distributed throughout the device and are arranged independently of each other. The problem to be considered here is that as long as the required rated residual moisture content is achieved in total at the end of the device, there is typically no harm in drying between two humidifying units. Advantageously, humidification between two dryings can also avoid the problem of paper hornification, so that even if the path between the two humidifying units and the drying unit that may be located between them is longer relative to the shortest path, the absorption rate that has been increased by the humidifying unit located further upstream is still continued on the humidifying unit located further downstream.

[0032] In a preferred embodiment, the device is a printing press, in particular a digital printing press. Additionally or alternatively, the processing unit is appropriately a printing unit that prints the web with ink, preferably with water-based ink and / or inkjet. Typically, the printing unit of a digital printing press has a plurality of printing bars, in particular for different colors (e.g., CMYK). Next, the drying unit of the printing press is a printing drying unit for ink drying. The multi-stage rehumidification described here is particularly suitable for printing presses, since here the web is usually dried intensively in order to dry the printed pattern generated during the ink printing. As a side effect, moisture is also removed from the paper, which is then replenished by rehumidification.

[0033] In a suitable embodiment, the device has a primer coating mechanism and a primer drying unit upstream of the printing unit, and a topcoat coating mechanism and a topcoat drying unit downstream of the printing unit. The primer coating mechanism is used for format processing, thereby applying a primer, especially as a substrate for subsequent printing. The applied primer is dried by the primer drying unit. Similarly, the topcoat coating mechanism is used for format processing, thereby applying a topcoat, especially as a final process of the printing previously performed. The applied topcoat is dried by the topcoat drying unit. The topcoat coating mechanism is analog, that is, the topcoat is applied or sprayed by a roller or a paint tank, or is digital, that is, the topcoat is printed by one or more printing rods like a digital printing unit. The primer coating mechanism and the topcoat coating mechanism are further equipment processing units.

[0034] Now, two humidifying units are appropriately arranged between the primer drying unit and the printing unit, or alternatively only one of the humidifying units is arranged. Alternatively or additionally, another humidifying unit is appropriately arranged between the printing drying unit and the topcoat coating mechanism, alternatively even two humidifying units are arranged. Alternatively or additionally, two further humidifying units are preferably arranged downstream of the topcoat drying unit, alternatively only one of the humidifying units is arranged. In a particularly preferred embodiment, the device has five humidifying units, wherein two humidifying units are arranged between the primer drying unit and the printing unit, another humidifying unit is arranged between the printing drying unit and the topcoat coating mechanism, and two further humidifying units are arranged downstream of the topcoat drying unit. Which of these humidifying units is the aforementioned first humidifying unit and the second humidifying unit is essentially arbitrary and will be appropriately set according to the specific operating mode, in particular according to the paper type and grammage. In principle, the two humidifying units between the primer drying unit and the printing unit are advantageously the first humidifying unit and the second humidifying unit for the pre-humidification and re-humidification, and / or the two humidifying units downstream of the topcoat drying unit are advantageously the first humidifying unit and the second humidifying unit for the pre-humidification and re-humidification. Next, before processing the web in the next processing unit, or before winding the web at the end of the equipment or handing it over to the subsequent equipment, an advantageous multi-stage re-humidification, especially a two-stage humidification stage, will be realized at the corresponding position.

[0035] If the web is not wound up at the end of the machine, but is transferred to a subsequent machine, such as a corrugated board machine, by means of a transfer section, a further, in particular a sixth, humidifying unit is advantageously arranged along the transfer section. The transfer section and the further humidifying unit are then in particular still components of the machine.

[0036] The operation of the individual humidifying units is not necessarily linked to the operation of the processing units located upstream thereof, but in a suitable embodiment, they can be humidified independently regardless of whether processing has been carried out previously. This is particularly advantageous if the drying unit upstream of the humidifying unit is active, or if the drying unit continues to function during order changes although the associated processing unit is inactive, since the web will then continue to be dried and re-humidification remains accordingly advantageous. For example, the primer coating mechanism is not required and activated for every order, so the primer coating mechanism may sometimes be inactive. In these cases, however, the primer drying unit continues to remain active and dries the web, which is then appropriately re-humidified with one or more downstream humidifying units before entering the printing unit or during the web entering the printing unit.

[0037] In a suitable embodiment, the device has an analog topcoat coating mechanism downstream of the printing unit, and additionally has a digital topcoat coating mechanism downstream of the analog topcoat coating mechanism. Optionally, the device has a primer coating mechanism and a primer drying unit upstream of the printing unit as described above. For analog and digital topcoat coating mechanisms, the above description applies. The device, in particular, has an additional topcoat drying unit downstream of the corresponding topcoat coating mechanism, by means of which the corresponding applied topcoat is dried. Preferably, one of the humidifying units is arranged between the printing unit and the analog topcoat coating mechanism (here downstream of the printing drying unit). Another humidifying unit is arranged between the analog topcoat coating mechanism and the digital topcoat coating mechanism (here downstream of the topcoat drying unit of the analog topcoat coating mechanism). Another humidifying unit is arranged downstream of the digital topcoat coating mechanism (more precisely, downstream of the topcoat drying unit for the digital topcoat coating mechanism). In this way, the device has a total of three humidifying units. Which of these humidifying units is the aforementioned first humidifying unit and the second humidifying unit is essentially arbitrary and will be appropriately set according to the specific operating mode, in particular according to the paper type and grammage. Advantageously, all three humidifying units can also be used together. Alternatively, one of the three humidifying units can be abandoned, so that the device then has only two humidifying units, which is already advantageous in itself.

[0038] In principle, it is advisable to arrange a humidifying unit at as many locations as possible in order to prevent the web from shrinking too much in the system and to maintain the dimensional accuracy of the web over the longest possible path in the system, thereby allowing one or more processing steps to benefit accordingly.

[0039] The device according to the invention is used for processing paper webs. The device comprises a processing unit for processing the webs and a drying unit arranged downstream of the processing unit for drying the webs. Furthermore, the device comprises a plurality of humidifying units arranged downstream of the drying unit, which are designed to rehumidify the webs with a humidifying agent in a plurality of stages, in that the webs are pre-humidified with a first humidifying unit and re-humidified with a second humidifying unit after a minimum residence time. The minimum residence time is accordingly selected so that the webs have a higher absorption rate of the humidifying agent in the second humidifying unit due to the pre-humidification. The above description also applies analogously to the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In the following, embodiments of the present invention are explained in detail according to the accompanying drawings.

[0041] Figure 1 The device is schematically shown;

[0042] Figure 2 The absorption of water by paper is schematically shown;

[0043] Figure 3 Schematically shows Figure 1 Variations of the equipment;

[0044] Figure 4 Schematically shows Figure 1 Another variation of the device. DETAILED DESCRIPTION

[0045] exist Figure 1 , Figure 3 and Figure 4 In each of the figures, a variation of the apparatus 2 for processing a paper web 4 is shown. Figure 3 and Figure 4 In the description, without limiting the generality, the device 2 is assumed to be a digital printing press for printing a single-layer paper web 4. However, the description related thereto is also similarly applicable to other devices 2, such as corrugated board devices and other webs 4, such as multi-layer paper webs 4.

[0046] The web 4 is guided through the device 2 and unwound, for example, by an unwinder of the device 2 (not shown in detail), then processed and finally rewound again by a rewinder 6 of the device 2 or alternatively directly handed over to a subsequent device (not shown) via a transfer section 8 .

[0047] The device 2 usually has a processing unit 10 for processing the web 4. In addition, downstream of the processing unit 10, the device 2 has a drying unit 12 for drying the web 4. The drying unit 12 has one or more hot air dryers 14 and / or infrared dryers 16 for drying. During drying, water is generally removed from the paper of the web 4, which should be replenished as completely as possible by rehumidification. For this purpose, downstream of the drying unit 12, the device 2 has a plurality of humidifying units 18, 20, by means of which the web 4 is rehumidified with a humidifying agent in a plurality of stages. The web 4 is rehumidified with a humidifying agent in a plurality of stages, by prehumidification with a first humidifying unit 18 and rehumidification with a second humidifying unit 20 after a minimum residence time T.

[0048] The moistening agent contains mainly water and additionally a mixture of water and moistening additives for reducing the surface tension of the water. Optionally, the moistening agent is additionally mixed with air or a similar medium.

[0049] The shortest residence time T is selected accordingly so that the web 4 has a higher absorption rate of the humidifying agent in the second humidifying unit 20 due to pre-humidification. Here, the principle that the humidifying agent first forms a liquid film on the web 4 during the pre-humidification process is used, which is not immediately absorbed by the paper due to the previous drying process, but at least partially stays there and takes at least a certain amount of time to be completely absorbed by the paper. During this period, it can be said that the web 4 has been flooded with humidifying agent, and it is meaningless to continue to supply humidifying agent because it cannot be absorbed by the paper. This is Figure 2 , which shows the absorption of the moistening agent in the web 4 at different times T1, T2, T3. Different markings are used for the moistening agent applied by pre-moistening B1 on the one hand and by re-moistening B2 on the other hand. For re-moistening, the absorption capacity A of the paper at different times T1, T2, T3 is also shown (this absorption capacity is a measure of the absorption rate). At the time T1 immediately following the pre-moistening, the liquid film forms a corresponding barrier and limits the maximum absorption capacity of the paper. The paper fibers 22 form a pore structure, which is flooded with the moistening agent from the pre-moistening B1, and re-moistening is therefore difficult. Figure 2 The enlarged view for time T1 in FIG shows in detail how water molecules are transported through the pore structure by capillary transport and then diffuse in the paper fibers 22. At time T2, the humidifying agent from pre-humidification has been completely absorbed by the paper, the pore structure has been pre-humidified, and the liquid film has been eliminated, the contact angle is especially 0, and the absorption rate is greater both relative to time T1 and the absorption rate before pre-humidification. At time T3, the absorption rate will still increase, and due to the expansion of the paper fibers 22, the pore structure becomes more closed, and the absorption capacity is slightly reduced again.

[0050] Accordingly, the rehumidification is divided into multiple stages, that is, it is distributed to at least two humidification units 18, 20, which then form a first rehumidification stage and a second rehumidification stage accordingly. Here, the actual target amount of humidifier is not used for prehumidification, but the amount of humidifier is reduced accordingly. The remaining humidifier is then provided during rehumidification. Since the web 4 is prehumidified, the humidifier of the second humidification unit 20 can be absorbed by the paper significantly faster than if no prehumidification is performed, so that the web 4 can absorb more humidifier in total on the same path compared to single-stage rehumidification.

[0051] The minimum residence time T is used to wait for a re-humidification moment that is as favorable as possible. As long as there is a liquid film on the web 4, the absorption rate for the continuously applied humidifying agent is practically equal to zero, which only increases after the liquid film is absorbed by the web. The minimum residence time T is therefore selected accordingly so that when the web 4 reaches the second humidifying unit 20, the humidifying agent applied by the first humidifying unit 18 has been completely absorbed by the web 4 (i.e., before the web 4 reaches the second humidifying unit 20). Figure 2 In particular, an increased absorption rate results here.

[0052] In this case, an increased absorption rate is first achieved in a first phase by means of pre-humidification. Once the absorption rate has increased significantly and, ideally, has reached a suitable absorption rate threshold, further moisture is added to the paper in a second phase by means of re-humidification, so that overall more moisture is added to the paper in the same time and path.

[0053] For example, the shortest dwell time is in the range of 0.5 s to 30 s. The shortest dwell time T corresponds to the shortest path that the web 4 travels between the first humidifying unit 18 and the second humidifying unit 20. The conversion between the shortest dwell time T and the shortest path is performed using the web speed, i.e. the speed at which the web 4 is transported through the device 2.

[0054] Typically, the amount of moisture that paper can absorb depends on the grammage of the paper (e.g., at 100 g / m 2 Up to 300g / m 2 ). It also usually depends on the type of paper. The higher the grammage, i.e. the heavier the paper, the more moisture the paper can absorb. Thus, for example, the amount of moistening agent applied to the web 4 per unit time by means of the humidifying units 18, 20 is set according to the grammage of the paper, wherein the amount is also increased for an increased grammage. Alternatively or additionally, the amount is set in a similar manner according to the type of paper.

[0055] In the embodiment shown here, a maximum of 3 g / m 2 is applied using the individual humidifying units 18 , 20 . 2Depending on the weight, one of the humidifying units 18 and 20 will be used to apply 1g / m 2 Up to 3g / m 2 Or a larger amount of humidifier. In addition, for example, at least 5 g / m 2 The web 4 can be re-moistened to a residual moisture content of at least 4% to at least 7% (ie, wt %), in particular depending on whether the paper is coated or uncoated.

[0056] exist Figure 3 and Figure 4 In the embodiment of the present invention, the humidifying units 18, 20 are respectively designed as spray bars. In principle, other embodiments can also be considered, such as a humidifying mechanism with a roller or a spray disk.

[0057] There are, in particular, a number of suitable embodiments for the arrangement of the humidifying units 18, 20 in the device 2, two of which are Figure 3 and Figure 4 The various aspects of these embodiments can in principle be combined with one another as desired.

[0058] Typically, the plant 2 has at least one plant section 24, which comprises the processing unit 10 and the drying unit 12. However, according to specific embodiments, and in particular in Figure 3 and Figure 4 In the embodiment, the device 2 may also have other device sections 24 that guide the web 4 in sequence. In this case, the winder 6 and the conveying section 8 are each the last device section 24. In particular, Figure 4 An embodiment is shown in which both a reel 6 and a conveying section 8 are present, from which one can be selected later depending on specific requirements (alternatively or additionally, a line operation is also achieved here).

[0059] exist Figure 3 and Figure 4 In the embodiment, the humidifying units 18, 20 are respectively arranged downstream of a corresponding cooling unit 26 of the device 2, which is arranged downstream of the corresponding drying unit 12. The cooling unit 26 after the drying unit 12 serves to recool the web 4. Now, the humidifying units 18, 20 are not integrated in the cooling unit 26, but are arranged independently at other locations.

[0060] In addition, especially in Figure 3 As can be seen in FIG. 1 , the web 4 is not dried and no processing is performed between the partial humidification units 18 and 20 , only transport is performed. Therefore, no other processing unit 10 or drying unit 12 is arranged between the first humidification unit 18 and the second humidification unit 20. Figure 3In the embodiment, the first humidifying unit 18 and the second humidifying unit 20 are arranged at the end of the equipment section 24, but other positions are also allowed and suitable. The first humidifying unit 18 and the second humidifying unit 20 and the shortest path between them are also collectively referred to as a two-stage humidifying section. Figure 3 The device 2 in the embodiment has two such two-stage humidification stages, and Figure 4 Device 2 in the example does not.

[0061] exist Figure 3 and Figure 4 In the embodiment, the device 2 has a plurality of device sections 24, each of which has a processing unit 10 and a subsequent drying unit 12, and at least one of the humidifying units 18, 20 is arranged downstream of the corresponding drying unit 12, so that the web 4 is humidified at least once after each drying and before the next drying or before the end of the device 2. Different from the two-stage humidifying section, the humidifying units 18, 20 are now distributed in the entire device 2 and are arranged independently of each other. Figure 4 This is particularly the case in the Figure 3 , since there too, a plurality of humidifying units 18 , 20 are arranged between the drying units 12 and at the end of the device 2 .

[0062] exist Figure 3 and 4 In the exemplary embodiment shown, the device 2 is a digital printing press, and one of the processing units 10 is a printing unit 28 for printing a web 4 with ink. The associated drying unit 12 is a printing drying unit 30 for drying ink. Figure 3 In the printing drying unit 30, for example, five infrared dryers 16 and four hot air dryers 18 are provided. Figure 4 In the figure, the printing and drying unit 30 is not shown in detail.

[0063] exist Figure 3 In the apparatus 2, upstream of the printing unit 28, there is a primer coating mechanism 32 and a primer drying unit 34, and downstream of the printing unit 28, there is a topcoat coating mechanism 36 and a topcoat drying unit 38. The primer coating mechanism 32 and the topcoat coating mechanism 36 are further processing units 10 of the apparatus 2. The primer is applied by the primer coating mechanism 32, which serves as a base for subsequent printing and is dried by the primer drying unit 34. Similarly, the topcoat is applied by the topcoat coating mechanism 36, which serves as a finishing process for the previously performed printing and is dried by the topcoat drying unit 38. The topcoat coating mechanism 36 is in Figure 3 In the figure, the topcoat is applied or sprayed by a roller or a paint tank. Alternatively, a digital topcoat application mechanism 40 is also suitable, that is, the topcoat is printed by one or more printing bars like a digital printing unit.

[0064] according to Figure 3 The device 2 shown has five humidifying units 18, 20, wherein two humidifying units 18, 20 are arranged between the primer drying unit 34 and the printing unit 28, another humidifying unit 18, 20 is arranged between the printing drying unit 30 and the topcoat application mechanism 36, and two further humidifying units 18, 20 are arranged downstream of the topcoat drying unit 38. Figure 3 In FIG. 1 , an exemplary association is also described, wherein the humidifying units 18 and 20 are the first humidifying unit 18 and the second humidifying unit 20 . However, this association can be changed in principle. Figure 3 In the figure, the two humidifying units 18, 20 between the primer drying unit 32 and the printing unit 28 are the first humidifying unit 18 and the second humidifying unit 20 for the pre-humidification and re-humidification, and the two humidifying units 18, 20 downstream of the topcoat drying unit 38 are also the first humidifying unit 18 and the second humidifying unit 20 for the pre-humidification and re-humidification. In this way, before the web 4 is processed in the next processing unit 10, or before the web 4 is rolled up at the end of the device 2 or transferred to the subsequent device, a multi-stage rehumidification, especially a two-stage humidification section, is achieved at the corresponding position. If the web 4 is not rolled up at the end of the device 2, but is transferred to the subsequent device, such as a corrugated board device, by means of the conveying section 8, another sixth humidifying unit 18, 20 (not shown here) can be optionally arranged along the conveying section 8.

[0065] according to Figure 4 The device 2 shown has an analog topcoat coating mechanism 36 downstream of the printing unit 28 and, downstream thereof, an additional digital topcoat coating mechanism 40. One of the humidifying units 18, 20 is arranged between the printing unit 28 and the analog topcoat coating mechanism 36, and another humidifying unit 18, 20 is arranged between the analog topcoat coating mechanism 36 and the digital topcoat coating mechanism 40. Another humidifying unit 18, 20 is arranged downstream of the digital topcoat coating mechanism 40. In this way, the device 2 has a total of three humidifying units 18, 20, and alternatively, one of the three humidifying units 18, 20 is abandoned, so that the device 2 then has only two humidifying units 18, 20.

[0066] Reference numerals list

[0067]

Claims

1. A method for rehumidifying a paper web (4), - wherein the web (4) is guided by the device (2), -in, The device (2) comprises a processing unit (10) for processing the web (4). - wherein the device (2) has a drying unit (12) for drying the web (4) downstream of the processing unit (10), - wherein the device (2) has a plurality of humidifying units (18, 20) arranged downstream of the drying unit (12), with the aid of which the web (4) is rehumidified with a humidifying agent in a plurality of stages, in that the web (4) is pre-humidified with a first humidifying unit (18) and the web (4) is re-humidified with a second humidifying unit (20) after a minimum residence time (T), - wherein the minimum residence time (T) is selected accordingly so that the web (4) has a higher absorption rate of the moistening agent in the second moistening unit (20) due to the pre-moistening.

2. The method according to claim 1, in, The shortest residence time (T) is selected accordingly so that when the web (4) reaches the second humidifying unit (20), the moistening agent applied by the first humidifying unit (18) has been completely absorbed by the web (4).

3. The method according to claim 1 or 2, in, The shortest residence time (T) is in the range of 0.5 s to 30 s.

4. The method according to any one of claims 1 to 3, in, The amount of humidifying agent applied to the web (4) per unit time by means of the humidifying unit (18, 20) is set according to the grammage of the paper. Among them, the dosage will also increase for the increased weight.

5. The method according to any one of claims 1 to 4, in, Use each of the humidifying units (18, 20) to apply up to 3 g / m 2 humidifier.

6. The method according to any one of claims 1 to 5, in, The humidifying unit (18, 20) is used to apply at least 5g / m 2 of moisturizing agent, or re-moistening the web (4) to a residual moisture content of at least 4%.

7. The method according to any one of claims 1 to 6, in, The humidifier is a mixture of water and humidifying additives.

8. The method according to any one of claims 1 to 7, in, The humidifying units (18, 20) are respectively designed as spray rods.

9. The method according to any one of claims 1 to 8, in, The humidifying unit (18, 20) is arranged downstream of the cooling unit (26), and the cooling unit (26) is arranged downstream of the drying unit (12).

10. The method according to any one of claims 1 to 9, in, The web (4) is not dried between the first moistening unit and the second moistening unit (18, 20).

11. The method according to any one of claims 1 to 10, in, The device (2) comprises a plurality of device sections (24), each of which comprises the processing unit (10) and the downstream drying unit (12). At least one of the humidifying units (18, 20) is arranged downstream of the drying unit (12), so that the web (4) is humidified after each drying.

12. The method according to any one of claims 1 to 11, in, The device (2) is a printing press, wherein the processing unit (10) is a printing unit (28) for printing the web (4) using ink, and the drying unit (12) is a printing drying unit (30) for drying the ink.

13. The method according to claim 12, in, The device (2) has a primer coating mechanism (32) and a primer drying unit (34) upstream of the printing unit (28), and has a topcoat coating mechanism (36, 40) and a topcoat drying unit (38) downstream of the printing unit (28). Wherein, two humidifying units (18, 20) are arranged between the primer drying unit (34) and the printing unit (28). Wherein, another humidifying unit (18, 20) is arranged between the printing drying unit (30) and the topcoat coating mechanism (36, 40), Wherein, two other humidifying units (18, 20) are arranged downstream of the topcoat drying unit (38).

14. The method according to claim 12, in, The device (2) has an analog topcoat coating mechanism (36) downstream of the printing unit (28), and a digital topcoat coating mechanism (40) downstream of the analog topcoat coating mechanism (36). Wherein, one of the humidifying units (18, 20) is arranged between the printing unit (28) and the analog topcoat coating mechanism (36), Wherein, another humidifying unit (18, 20) is arranged between the analog topcoat coating mechanism (36) and the digital topcoat coating mechanism (40), The other humidifying unit (18, 20) is arranged downstream of the digital topcoat coating mechanism (40).

15. A device (2) for processing a paper format (4), - having a processing unit (10) for processing the web (4), - having a drying unit (12) arranged downstream of the processing unit (10) for drying the web (4), - having a plurality of humidifying units (18, 20) arranged downstream of the drying unit (12), which are designed to rehumidify the web (4) with a humidifying agent in a plurality of stages, in that the web (4) is pre-humidified with a first humidifying unit (18) and the web (4) is re-humidified with a second humidifying unit (20) after a minimum residence time (T), -in, The shortest residence time (T) is selected accordingly so that the web (4) has a higher absorption rate of the moistening agent in the second moistening unit (20) due to the pre-moistening.

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